Take sugar and water in a medium pot and bring it to the boil. Boil it for ten minutes over medium-high heat. Then add the lemon juice and boil it for another 5 minutes. Turn the heat off and set aside.Take kataifi from the freezer and break into small pieces in a mixing bowl immediately. Let it thaw for ten minutes. Then add melted butter in it and mix it evenly. Take 1+ 1/2 tbsp of kataifi in a Turkish coffee cup (or a muffin cup) and make an indentation. Fill the indentation with 1 tbsp of diced walnut and close it up with 1/2 tbsp of kataifi and press. Turn the cup into baking dish and gently take the cup off. Repeat these steps until kataifi is finished.Preheat the oven 350 F. Bake it until it is golden brown. Take it from oven and spoon the cold syrup over it. Let it cool.